Tracking down starflight in literature is an absorbing pastime. When I was writing my Centauri Dreams book, I found that I was vaguely familiar with many of the antecedents of today’s science fictional journeys, but a book called Wunderwelten, by Friedrich Wilhelm Mader, took me by surprise. A 1911 adventure novel for young readers, Wunderwelten imagines a sphere that, in the fashion of the time’s space fiction, was moved by antigravity in a multi-year journey to Alpha Centauri. Mader’s ship, called ‘Sannah,’ was a precursor to all the Centauri-bound starships to come.
What a delight to find Sannah emerge in the form of Sannah III in Stephen Baxter’s story “Star Call,” which appears in the recently published Starship Century. But Baxter’s updated ship is a far cry from the 50-meter antigravity vessel imagined by Mader. For one thing, it’s gifted with artificial intelligence:
I am called Sannah III because I am the third of four copies who were created in the NuMind Laboratory at the NASA Ames research base. I was the one who was most keen to volunteer for this duty. One of my sisters will be kept at NASA Ames as backup and mirror, which means that if anything goes wrong with me the sentience engineers will study her to help me. The other sisters will be assigned to different tasks. I want you to know that I understand that I will not come home from this mission. I chose this path freely. I believe it is a worthy cause.
Image: Science fiction novelist Stephen Baxter, who has revived Mader’s antique starship.
Sannah’s cause, and the thinking around it, are regularly reported back to Earth as it travels, all by means of the Star Call system, which allows people to buy a share in the mission and in return get once-a-decade message exchanges with the starship. A poignancy in these communiques emerges that reminds me of Greg Bear’s sentient starship in Queen of Angels as we begin to realize the mission is not going well and Sannah may not have all the facts.
Emergence of Pellet Propulsion
Interestingly, the stardrive on Sannah is not antimatter but what Baxter dubs a ‘Singer-Nordley-Crowl’ drive after Clifford Singer, who studied pellet propulsion technologies back in the late 1970s. The Nordley reference is to Gerald Nordley, whose own pellet propulsion methods revised and significantly upgraded Singer to allow for ‘smart pellets’ with course correction. Crowl, of course, is our own Adam Crowl, who has been writing and commenting on this site almost since its inception, and whose own entry in Starship Century is a comprehensive look at how researchers have envisioned starships in our time.
Adam, serious congratulations, buddy. I mean, to have a stardrive named after you…
Nordley was interested in nanotechnology and proposed that the problems of getting small particles moving at relativistic speeds to their target (where they would push against its magnetic field to drive it forward) could be handled by artificial intelligence and minute rockets. ‘Smart pellets’ wouldn’t be easy to send on their way but nanotechnology worked there as well. Says Crowl:
To power either system would require immense solar power-collection systems, which Nordley proposed to be built via self-replicating machines. Optimistically assuming a single self-replicating power-satellite that supplies one gigawatt of power that copies itself in a year, then within mere decades sufficient power would be available to propel a 1,000-ton starship to 0.86c at five-Gs, and a decade later a thousand such starships could be propelled per year.
0.86c is an interesting figure. Nordley told me in an interview years back that he thought the first human crew to reach Alpha Centauri would get there after a journey lasting about three years. That’s three years as experienced by the crew. Moving at 0.86c, he added, those aboard the starship would experience a time compression factor of two — half as much time would expire for them as would expire for the people left behind on Earth. Add in acceleration and deceleration time and you get the result, a three year passage (as perceived by those onboard) to the nearest star. It’s about the same amount of time it took Magellan to circumnavigate the Earth.
Image: Interstellar researcher Gerald Nordley, speaking at the Space Access 2010 Conference in Phoenix, Arizona.
Interactions with the Medium
Crowl’s paper runs through all the starship concepts I’ve ever encountered, among the most fascinating of which are the lesser known. Back in the 1970s, for example, as NASA studied the possibility of pushing a probe up to interstellar speeds using lasers, Philip C. Norem and Robert Forward went to work on the question of how to slow down a probe for rendezvous. One of Forward’s sail deceleration concepts was ingenious enough to merit separate treatment, and I’ll talk about it tomorrow as we discuss Jim Benford’s ideas on laser and microwave sails. But there are other ways of doing these things, and Norem and Forward found that a starship could be turned by using large charged wires to interact with the galactic magnetic field.
The key to this is the fact that a charged object moving through a magnetic field experiences a Lorentz force at right angles to its direction of motion and the magnetic field itself. If you give it enough time to work, the Forward/Norem method can actually slow a probe down and turn it so that it approaches the target star (from our perspective on Earth) from behind. At that point a laser beam from Earth could be trained on the starship’s sail to slow it for the rendezvous. The same method could be used in reverse to enable a return journey. The main problem is that the large turning circles require centuries of additional travel time to pull off the feat.
Both Forward and Norem were fascinated by the concept of ‘thrustless turning,’ written up by Norem in a 1969 paper. I’ll mention another aspect of this that may be germane here, a 2005 paper by Gregory Matloff and Les Johnson that studies how to use the interstellar medium not for turning but for generating power aboard the spacecraft. This could be done through the interactions between an electrodynamic tether and the interstellar magnetic field.
We might throw Freeman Dyson into the mix as well. Dyson studied propellantless braking after observing the magnetic interactions between the large inflatable satellites of the early 1960s and the plasma around them. A starship using these methods to decelerate would release electromagnetic energy that might be observable, thus allowing a search for extraterrestrial space vehicles. Crowl discusses what Dyson called Alfven braking in relation to magnetic sail concepts that emerged in the late 1980s. And it’s to sails, though not magnetic ones, that I want to turn tomorrow as we ponder Crowl’s many propulsion alternatives.
The Philip Norem paper is “Interstellar Travel: A Round Trip Propulsion System with Relativistic Capabilities,” AAS 69-388 (June, 1969). Robert Forward’s paper on Lorentz force turning is “Zero-Thrust Velocity Vector Control for Interstellar Probes: Lorentz Force Navigation and Circling,” AIAA Journal 2 (1964), pp. 885-889. Gregory Matloff and Les Johnson write about electrodynamic tether possibilities in “Applications of the Electrodynamic Tether to Interstellar Travel,” JBIS 58 (June, 2005), pp. 398-402. Cliff Singer’s first pellet paper is “Interstellar Propulsion Using a Pellet Stream for Momentum Transfer,” JBIS 33 (1980), pp. 107–115.
I wonder how ling it’ll take for someone to notice that Sannah III is as much a nod to A.C.Clarke, with the similarity of redundant AIs on the ground, and that the mission AI doesn’t have all the facts- much like HAL 9000… :)
(Or that Baxter worked with Clarke, for that matter, hence the “nod”… ;) )
Interesting that in the story, Sannah III acknowledges she won’t come “home” from the mission.
That made me smile. What can we possibly imagine the concept of “home” will mean to a truly awake AI?
I wonder if there will end up being a connection:
1. There’s been a lot of speculation regarding the when and how of the predicted AI Singularity, both in SF and in speculative essays.
2. There’s been a lot of speculation (attested here on this website) of the when and how of star travel.
I wonder if those two separate lines of speculation will end up converging as the speculation approaches reality.
Just a thought.
The use of pellets is a propulsion method I would like to investigate for the I4IS. The pellets are smart and will auto track the spacecraft using on board micro/nano electronic circuits and use gas stored as a solid to course correct before impacting as a cloud on the sail of the craft. The solid could be designed to include materials from which the space crafts sail area can be increased using nano/micro assemblers as it moves towards the target improving the gas catchment area.
On the issue of how one moves through the medium…I’ve been re-reading (having discovered the efficiency of audiobooks during my daily beach run) Hamilton’s Pandora’s Star and Judas Unchained, both of which depend on a charming concept: stable wormholes provide ‘walk-thru’ access to other places. An entire infrastructure of railroads is established, thereby obviating the messy necessity of interstellar travel!
Outlandish, you might ask? Perhaps. Who knows? And that’s the point of speculative fiction, isn’t it? Providing a background for the exploration of human culture in some distant setting?
Jack McDevitt recently wondered about Earth in the far future on his website, asking what we will eat in the 11th millennium. It’s a question at least as interesting as how we get to another star.
And Paul: the recent Hugo awards contained several nominees that dealt with our favorite subject here, namely how the heck do we get there. Alas, a short-lived but popular book won, but still, there are plenty of worth ideas in the list.
It’s interesting, but it seems a little too optimistic and lack important details, making it highly unlike to happen. A velocity of 0.86c is too high, the faster you go stronger will be the impact with interstellar dust, it would be like bombs, i wouldn’t put my hopes on such extreme velocities, i guess just there’s no way we can achieve 0.5c or higher, in fact i don’t believe we’ll get even at 0.3c. The most realistic speed i can think it’s something between 0.1 and 0.2c, where we do not experience significant effects of time dilatation.
Anything better than that might be new exotic ways of propulsion, like warp drives or something like that. That’s how i see it, and on near term i think we should stop using chemical rockets once for all, because they have no future for deeper space, and go for ion engines and other more efficient propulsion techniques.
Michael Spencer writes:
Michael, give us some titles you’d recommend here. Would love to look into these.
0.86 C while quite attractive is probably beyond our means. Not only energy wise it’s hard to imagine a spaceship with a crew that would be realistically possible, but the possible collisions with even smallest pieces of matter would be extremely destructive. Maybe some kind of small probe would be able to travel that fast, but its limited capabilities wouldn’t make the immense effort worthwhile compared to telescopes.
For me speeds like 0.1 up to 0.3 remain most realistic and quite sufficient for interstellar travel to nearby systems.
Doubt can be an impediment if it stops the search for solutions. Gerald Nordley has pondered most of the questions you ask, as have many other researchers. There are ways of mitigating the impact hazard – a reasonable concept is to fly behind a precursor that possible impactors are ionised by, then deflect the resulting particles via magnetic fields. During boost-phase the propulsion system which ionises the momentum transfer pellets “leaks” plasma in the forward direction, which also acts to ward off impinging impactors. Another useful process is dust deflection via the vehicle’s magnetic fields as most interstellar dust has an acquired surface charge from cosmic rays and UV light. A combination of systems can mitigate against the hazards.
This is an attractive approach. The tough nut on which to concentrate is how to accelerate the pellet. The fastest we can accelerate pellets (aka bullets) today is around 2-3 km/s. Many, many orders of magnitude to go with all sorts of fundamental barriers to break down or circumvent. Jordan Kare’s sailbeam concept is a good path forward, here, in my opinion.
I am not sure, but it seems to me that larger dust grains would be VERY rare, and we may end out with a situation where an impact would be catastrophic, but not expected. Similar to how we operate in interplanetary space today.
By far most of the interstellar medium is gas (99%), which produces steady abrasion and at higher velocities (~0.3c or so) a great amount of heat. A thick shield in front of the craft can take care of the abrasion (tungsten or carbon or such) and radiate the heat away simply by being very hot.
That said, I think your estimates on the difficulty of achieving relativistic velocities is quite reasonable.
Unfortunately, it is the other way around. The smaller the probe, the more difficult it gets to reach relativistic velocities. This is mostly because the thickness of the required shield is independent of the mass of the probe.